A conventional one-dimensional bar code cannot store a large quantity of data. With the popularization of input/output devices such printers, scanners and digital cameras, studies on a 2-dimensional bar code capable of storing larger amount of data than the one-dimensional bar code are being actively carried out. That is, attempts to improve efficiency and convenience in transmission and representation of data using the 2-dimensional bar code are being made in various fields.
The 2-dimensional bar code used for the attempts should be generated without having restrictions on its size and store a large quantity of data per unit area. Furthermore, the 2-dimensional bar code requires short recognition time and excellent decoding capability when decoded. The 2-dimensional bar code can be used only in a restricted field unless these conditions are satisfied.
FIGS. 1a and 1b illustrate 2-dimensional bar codes using Maxi code among conventional standard 2-dimensional bar codes. Referring to FIGS. 1a and 1b, the Maxi code is composed of a central finder pattern surrounded by a tetragonal arrangement of hexagonal module offset rows. The finder pattern includes three black concentric circles, and information about direction can be known from six patterns (inside the circles) composed of three modules at the corners of a hexagon. However, the Maxi code requires long recognition time because all the six patterns should be searched when patterns about direction are searched.
FIG. 1c illustrates a 2-dimensional bar code using QR code among the conventional standard 2-dimensional bar codes. Referring to FIG. 1c, a finder pattern of the QR code is composed of three identical position detection patterns respectively disposed at the left top, right top and left bottom of a symbol. The QR code symbol has been encoded preferentially such that probability that similar patterns come into contact with the region outside the symbol is low, to enable rapid recognition. Furthermore, recognition of the three position detection patterns constructing the finder pattern correctly defines the direction of the symbol position in the range of vision.
In the case of the QR code, however, all the three position detection patterns should be searched and, when any one of the position detection patterns is damaged, the position and direction of the symbol are difficult to define.
The aforementioned conventional 2-dimensional bar codes have following problems. Firstly, the sizes of the conventional 2-dimensional bar codes should be increased to store large capacity because capacity per unit area is small, and a long period of bar code search time is required when the 2-dimensional bar codes are recognized. Furthermore, the sizes of the conventional 2-dimensional bar codes are fixed when generated or difficult to set and thus they cannot be applied to various fields. Accordingly, it is difficult to realize large capacity data such as text data, photograph data and audio data in the form of the conventional 2-dimensional bar codes so that the conventional 2-dimensional bar codes have been applied to only a specific field.
While there is a method of adding colors and gray to a conventional black-and-white 2-dimensional bar code to increase capacity, correct decoding cannot be performed in this case because a difference between the color of print and the original color is generated.